With the technical and business progress in mobile data traffic, people have noticed that over 70% of the wireless services are consumed indoor. Current dominant indoor wireless access schemes are either of distributed antenna system (DAS) or small cell system. However, there are shortcomings in both of these approaches. For DAS, the data streams fed to/from different antennas are the same, making this scheme good for coverage and cost friendly in deployment but restricted in capacity. For indoor small cell system, since Base Band Unit (BBU) is distributed and co-located together with the radio head, it makes the radio heads very complex and costly on the one hand, and makes wireless coordination among radio heads like coordinated multiple-point (CoMP), massive (multiple-input multiple-output) MIMO incompatible on the other hand.
Comparing to the rapid progress and development pace in wireless communication, its corresponding fronthaul/backhaul strategies based on fixed network technology still lag behind, especially in terms of capacity, feasibility and compatibility. In convention, fiber to the home (FTTH) was once regarded to be a large capacity solution of fixed network and can meet the requirements of accommodating wireless access services. However, FTTH turns out to be suboptimal or incapable for in-building deployment where the antenna heads are in scattering distribution across the rooms and floors and the fiber can't reach with ease and cost efficiency. Therefore, indoor coaxial cables have been chosen as the last 100 meter fixed fronthaul link between the FTTH and the indoor antenna heads. The main reason that makes indoor cable a preferred option as the junction between the radio interface and fiber in the range of about 100 meters is mainly based on the fact that within this range well shielded coaxial cable provides a wide and flat spectrum response with acceptable attenuation and robustness.
However, the present available indoor coverage approach, e.g., DAS on the one hand is weak in throughput capacity since the data to each antenna are identical, and MIMO therefore is not compatible in DAS; on the other hand, current DAS is not economical since costly coaxial cables are used.
Therefore, there is an urgent request on finding a reliable and feasible solution for indoor wireless access and transport over fixed network architectures with the following requests to be fully met: cost efficiency on fixed transport networks with large capacity for wireless x-hauling; and good compatibility to MIMO, CoMP or/and other advanced wireless technologies.
There has been rare of good solutions reported yet for BBU centralized indoor wireless access deployment with long reach fronthaul transport over reliable and cost-efficient fixed networks so far.